Hydroconversion reactions, including hydrotreating and hydrocracking, may be used to upgrade a hydrocarbon feedstock by increasing its hydrogen content, removing various heteroatom contaminants, and/or converting longer-chain hydrocarbon molecules into shorter-chain hydrocarbon molecules. A hydroconversion catalyst is typically used to catalyze one or more hydroconversion reactions between hydrogen and the hydrocarbon feedstock.
The performance of a hydroconversion reaction, including the reaction rates, the hydrocarbon conversion and the formation of undesirable byproducts, depends to a great extent upon the activity and selectivity of the hydroconversion catalyst. For example, a fresh catalyst may support high reaction rates and high hydrocarbon conversion. However, over time, the activity of the hydroconversion catalyst may decrease due to various coking mechanisms, including carbon laydown, pore mouth plugging, and loss of interstitial pore volume.
Fresh hydroconversion catalyst is especially prone to excessive coking when subjected to a high-severity environment, including high temperature, high pressure, and a hydrocarbon feed having a high concentration of sulfur. For example, a fresh unconditioned/un-presulfided hydroconversion catalyst may loose as much as half of its activity or more when it is sulfided in the high severity environment existing in the hydroconversion reactor. Under such conditions the unsulfided catalyst is subjected to a thermal shock. Such premature deactivation of the fresh hydroconversion catalyst may cause reduced hydrocarbon conversion and require more frequent catalyst change-outs and/or regenerations. Accordingly, various pre-treatment methods, including pre-sulfiding and/or preconditioning, are used to mitigate the effects of thermal shock on a hydroconversion catalyst.
The benefits of catalyst presulfiding in general are well known in the prior art. For example, the use of high boiling oils, such as vacuum gas oils, and hydrocarbon solvents to aid the incorporation of elemental sulfur into a catalyst is disclosed in U.S. Pat. No. 4,943,547. U.S. Pat. No. 4,530,917 discloses a method of presulfurizing a hydrotreating catalyst with organic polysulfides.
U.S. Pat. No. 4,177,136 discloses a method of catalyst presulfurizing wherein a catalyst is treated with elemental sulfur. Hydrogen is then used as a reducing agent to convert the elemental sulfur to hydrogen sulfide in situ. U.S. Pat. No. 4,089,930 also discloses the pretreatment of a catalyst with elemental sulfur in the presence of hydrogen. U.S. Pat. No. 6,291,391 discloses a process for pre-sulfiding using a hydrogen-sulfide containing gas and subsequently pre-conditioning the catalyst with a liquid hydrocarbon conditioning oil.
U.S. Pat. No. 4,443,330 discloses a process for maintaining activity of a catalyst during use in coal liquid upgrading process. An added sulfur-containing liquid is added to the reactor to stabilize and maintain the sulfur level in the reactor.
Each of the aforementioned processes for presulfiding a hydroconversion catalyst requires one or more of use of added noxious and/or toxic sulfur-containing compounds, equipment for the storage, feeding, and/or separation of said sulfur-containing compounds or elemental sulfur, additional hydrocarbons and/or solvents used during the pre-sulfiding of the catalyst, and other components or chemicals that add to the capital and operating expenses associated with hydroconversion processes.
Accordingly, there exists a need for efficient and compatible methods of pre-treating a hydroconversion catalyst.